The present invention relates to an image pickup tube, and more particularly to a stripeshaped color separation optical filter provided on one side surface of a transparent glass window of the image pickup tube and a method for manufacturing the same.
As is known, an image pickup tube provided with a stripe-shaped color separation filter is, for example, the one for a single tube or dual tube type color television camera. Typically, a television camera device including an image pickup tube such as single tube or dual tube type color image pickup tube is provided with a focusing coil and a deflection yoke around an envelope containing an electron gun. At the end of the envelope there are successively provided a photoconductive film, a transparent conductive film and a stripe-shaped color separation filter. The filter comprises two components one of which includes first narrow stripe-shaped elements substantially permitting all color lights from an object to pass therethrough and second narrow stripeshaped elements substantially preventing red color light of the color lights from the object from passing therethrough, the first and second elements being arranged in alternate relation to each other, and the other of which includes third narrow stripe-shaped elements substantially permitting all the color lights from the object to pass therethrough and fourth narrow stripe-shaped elements substantially preventing blue color light of the color lights from the object from passing therethrough, the third and fourth elements being arranged in alternate relation to each other.
Usually, the fourth elements are formed on the second elements without forming the first and third elements. Consequently, the thus formed filter necessarily has its surface indented at a number of positions. For this reason, the direct formation of the transparent conductive film and the photoconductive film on such an indented surface of the filter causes these films to have their surfaces also indented, resulting in the local variation of dark current upon operation of the image pickup tube. Thus, spurious signals are superimposed on the signals derived from the color lights from the object with the result that hindrances such as the generation of the spurious color signals occur. As mentioned above, the formation of the transparent conductive film and photo-conductive film on the filter having such an indented surface results in reduced yield on manufacturing steps.